The Acer U5520B has a noise level of 29dB, but the Hitachi CP -AW3005 is a 36dB noise level projector (7dB louder).
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The noise level of the projector is the amount of noise that the projector makes (caused by the cooling fan inside the projector) when it is running.

A lower noise level means that the projector will be quieter when it is running. This means that you will be able to appreciate the quieter parts of films better without the background noise of the projector running.

20% higher RMS rated power
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The Acer U5520B is a 20W RMS rated power projector. That's 4W higher than the Hitachi CP -AW3005 (16W).

Two built-in speakers
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The number of built-in speakers on the Acer U5520B is two, but the Hitachi CP -AW3005 only has one built-in speaker.

Available from 8 shops

The more stores stock this projector, the greater competition amongst stores to keep prices low.

The Hitachi CP -AW3005 has a noise level of 36dB, whereas the Acer U5520B is a 29dB noise level projector (7dB quieter).
Read more

The noise level of the projector is the amount of noise that the projector makes (caused by the cooling fan inside the projector) when it is running.

A lower noise level means that the projector will be quieter when it is running. This means that you will be able to appreciate the quieter parts of films better without the background noise of the projector running.

Lower RMS rated power
Edit

The Hitachi CP -AW3005 is a 16W RMS rated power projector. That's 4W lower than the Acer U5520B (16W).

Only one built-in speaker
Edit

The Hitachi CP -AW3005 is a one built-in speaker projector, whereas the Acer U5520B only has two built-in speakers.